The present invention relates in general to alkylated phenols and specifically to catalyzed pressure reactions of olefins with phenols to produce alkylated phenols.
Alkylated phenols are widely used as antioxidants for various substrates, as building blocks for polymers, as intermediates for the production of a wide variety of products, and for other specific end uses. Of particular importance are the mono- and di- orthoalkylated phenols. The compound 2,6-di-tert-butylphenol, for example, has been widely used for the production of various diphenols and for the well-known 4,4'-methylenebis(2,6-di-tert-butylphenol)antioxidant.
The compound 2,6-di-tert-butylphenol and various 2,6-di-alkylphenols may be synthesized by various catalytic routes including the pressure reaction of an olefin with phenol in the presence of a catalyst. Such processes typically produce a substantial portion of para-alkylated phenols which have only limited applications and are generally available in great quantity but must nevertheless be burned to obtain merely their fuel value. As used herein the term "para-alkylphenol" means any phenol having at least a para-alkyl substituent. These para-alkylphenols include para-tert-butylphenol, para-isopropylphenol, 2,4-di-sec-butylphenol, 2,4-di-tert-butylphenol, 2,4-diisopropylphenol, 2-isopropyl-4-tert-butylphenol, 2,4,6-triisopropylphenol, 2,4,6-tri-tert-butylphenol, 2,4,6-tri-sec-butylphenol, and various other compounds.
The aluminum phenoxide catalyzed reaction of an olefin gas with phenol is carried out by heating about 100 parts by weight phenol with about 1 part fresh aluminum metal at about 150.degree. C. to form an aluminum phenoxide catalyst and thereafter reacting the phenol containing the catalyst with a C.sub.3 or higher olefin usually at high pressure up to about 1,000 psig, for anywhere from about 15 minutes to a few hours so as to alkylate the phenol to form the desired product 2,6-dialkylphenol wherein the alkyl groups are secondary or tertiary. The catalyst in the resultant reaction mixture is killed and the reaction mixture is typically distilled to remove light ends including unreacted phenol and, subsequently, 2,6-dialkylphenol product, leaving 2,4-dialkylphenol and 2,4,6-trialkylphenol in the bottoms.
Typically, the light ends from the first distillation of the resultant reaction mixture contain some ortho-tert-butylphenol and some para-tert-butylphenol as well as, mainly, unreacted phenol. Any olefin gas coming overhead is recovered by a venting process and condensed for reuse. The overhead light ends may be recycled for reaction in the aluminum phenoxide catalyzed pressure reaction to make additional 2,6-dialkylphenol.
The subsequent distillation after removal of the light ends typically permits recovery of the product 2,6-dialkylphenol from the top of a second column and generates a column bottom stream containing the isomer 2,4-dialkylphenol and the homolog 2,4,6-trialkylphenol as well as a portion of product 2,6-dialkylphenol. Typically, the column bottoms also contain small portions of materials which appear to be biphenols, higher alkyl-substituted phenols (higher than expected from the olefin used), and some meta-substituted phenols.
The typical aluminum phenoxide catalyzed reaction described above results in the production of about 10-12 weight percent based upon the amount of phenol of para-alkylated phenols i.e., alkylphenols having substituents in the 4- position, especially 2,4-dialkylphenol and 2,4,6-trialkylphenol. Such a stream is often subjected to a dealkylation reactor in an attempt to recover additional phenol and olefin or used as a fuel source to at least recover its heat value.